Carbon fiber-containing resin dispersion solution and resin composite material

ABSTRACT

A vapor-grown-carbon-fiber-containing dispersion containing vapor grown carbon fiber having a fiber diameter of and an aspect ration of 5 to 15,000, a resin soluble in an organic solvent, and an organic solvent having an ET value of 45 or less, which value is a solvent parameter calculated from the absorption spectrum of pyridinium-N-phenol betaine, wherein (1) lumps of the carbon fiber are partially disintegrated to thereby allow individual filaments of the carbon fiber to be present as dispersed or (2) the carbon fiber is present such that carbon fiber lumps having a diameter of 40 μm or less and separated individual carbon fiber filaments are intermingled; a production method of the dispersion; vapor-grown-carbon-fiber-containing resin composite material obtained by the method; and electroconductive material and thermal conductive material using the resin composite material. The present invention enables to prepare a resin solution wherein vapor grown carbon fiber is uniformly dispersed and to easily obtain electroconductive material and thermal conductive material from the dispersed solution.

CROSS REFERENCE TO THE RELATED APPLICATIONS

This is an application filed pursuant to 35 U.S.C. Section 111(a) withclaiming the benefit of U.S. Provisional application Ser. No. 60/467,155filed May 2, 2003 under the provision of 35 U.S.C. Section 111(b),pursuant to 35 U.S.C. Section 119(e)(1).

TECHNICAL FIELD

The present invention relates to a dispersion containing vapor growncarbon fiber. More particularly, the present invention relates to avapor-grown-carbon-fiber-containing dispersion in which vapor growncarbon fiber is uniformly dispersed in a resin, to a method forpreparing the dispersion, to a resin composite material produced by useof the dispersion in which the vapor grown carbon fiber is uniformlyadmixed, to a method for preparing the resin composite material, and touse of the resin composite material (as an electroconductive material ora thermal conductive material).

BACKGROUND ART

Dispersing carbon fiber in a matrix such as a resin is a widely andcommonly performed technique for imparting electroconductivity orthermal conductivity to an object. Among carbon fibers, vapor growncarbon fiber is particularly useful, in that addition of only a smallamount thereof to a resin greatly improves electroconductivity andthermal conductivity, without adversely affecting processing-relatedcharacteristics of the resultant resin composition and the appearance ofa molded product (Japanese Patent No. 2862578 (U.S. Pat. No.5,643,990)).

When carbon fiber is incorporated into resin, mixing must be performedso that carbon fiber is uniformly present in the resin. Generally, suchmixing of carbon fiber into resin is carried out through a method inwhich carbon fiber is added to molten resin, followed by kneading by useof a twin screw extruder or a modified screw barrel. However, in orderto uniformly mix in a resin irregular-shaped vapor grown fine carbonfiber having a fiber diameter of 0.001 to 5 μm and a ratio of fiberlength to fiber diameter (aspect ratio) of 5 to 15,000, the meltkneading method involves problems, in that much power is required andbreakage of vapor grown carbon fiber occurs during kneading.

Therefore, in an attempt to provide a more convenient method forattaining a uniform mixture of vapor grown fine carbon fiber in resin,the present inventors have focused on preparation of a dispersion inwhich fine carbon fiber is uniformly dispersed in an organic solvent ofa thermoplastic resin. If a uniform dispersion of fine carbon fiber in athermoplastic resin can be obtained, the dispersion may be applied to anobject such as a substrate material by coating, spraying, immersing,etc., after which the solvent may be removed by drying, to therebyeasily produce a thermoplastic resin composition (composite), which hasfine carbon fiber uniformly dispersed therein on the substrate, as amaterial having functions for electroconductive or thermal conductivitematerial.

As a prior art reference related to a dispersion system of carbon fiberin an organic solvent, Japanese Patent Publication (kokai) No.2002-255528 discloses a micro particle dispersion prepared by dispersingfine particles in a bipolar aprotic solvent (dimethylsulfoxide,dimethylformamide or acetonitrile). Carbon nanotubes having a size ofabout 10 nm to 10 μm are mentioned in the publication as an example ofmicro particles. However, when the present inventors performed using abipolar aprotic solvent (dimethylformamide) disclosed in thepublication, no uniform dispersion can be obtained with respect to vaporgrown carbon fiber. Moreover, when vapor grown carbon fiber wasdispersed in a single solvent of tetrahydrofuran, benzene ordichloromethane through mechanical stirring, lumps of vapor grown carbonfiber that were initially present did not disintegrate and failed toyield a dispersion.

DISCLOSURE OF THE INVENTION

Accordingly, an objective of the present invention is to provide adispersion in which vapor grown carbon fiber having a fiber diameter of0.001 to 5 μm and an aspect ratio of 5 to 15,000 is uniformly dispersedin a resin, and a production method thereof.

Further objective of the present invention is to provide a resincomposition produced by use of the above-mentioned dispersion in whichthe vapor grown carbon fiber is uniformly admixed, a production methodthereof, and use, as an electroconductive material or a thermalconductive material, of the resin composite material obtained from theabove-mentioned dispersion through, for example, coating.

In view of the foregoing, the present inventors have continued extensivestudies, and have found that a resin solution in which vapor growncarbon fiber is uniformly dispersed is easily obtained by employment, asa resin, a polymer containing as its repeating unit a structural unithaving at least a cyclic structure, and a certain organic solvent havingan ET value of 45 or less, which value is a solvent parameter calculatedfrom the absorption spectrum of pyridinium-N-phenol betaine(“Shin-jikken Kagaku Koza” (“New Experimental Chemistry”) 14 (V), 2594(1978); Ann., 661, 1 (1963)), and have accomplished the invention.

Accordingly, the present invention relates to a dispersion containingvapor grown carbon fiber and a production method thereof, and to anelectroconductive material and a thermal conductive material producedusing a resin composite material prepared from the dispersion system, asdescribed below.

1. A vapor-grown-carbon-fiber-containing dispersion containing vaporgrown carbon fiber having a fiber diameter of 0.001 to 5 μm and anaspect ratio of 5 to 15,000, a resin soluble in an organic solvent andan organic solvent, wherein lumps of the carbon fiber are partiallydisintegrated to thereby allow separated individual filaments of thecarbon fiber to be present as dispersed.

2. A vapor-grown-carbon-fiber-containing dispersion containing vaporgrown carbon fiber having a fiber diameter of 0.001 to 5 μm and anaspect ratio of 5 to 15,000, a resin soluble in an organic solvent andan organic solvent, wherein the carbon fiber is present such that carbonfiber lumps having a diameter of 40 μm or less and separated individualcarbon fiber filaments are intermingled.

3. The vapor-grown-carbon-fiber-containing dispersion as recited in 1 or2 above, wherein the vapor grown carbon fiber contains 0.001 to 5 mass %of boron.

4. The vapor-grown-carbon-fiber-containing dispersion as recited in anyof 1 through 3 above, wherein the resin soluble in an organic solvent isa resin comprising a polymer having a structural repeating unit which atleast partially contains a cyclic structure.

5. The vapor-grown-carbon-fiber-containing dispersion as recited in anyof 1 through 4 above, wherein the resin soluble in an organic solvent isany of polystyrene, polycarbonate, polyarylate, polysulfone,polyether-imide, polyethylene terephthalate, polyphenylene oxide,polyphenylene sulfide, polybutylene terephthalate, polyimide,polyamidoimide, polyether-ether-ketone, or polyamic acid, or a mixturethereof.

6. The vapor-grown-carbon-fiber-containing dispersion as recited in anyof 1 through 5 above, wherein the organic solvent has an ET value of 45or less, where the ET value is a solvent parameter calculated from theabsorption spectrum of pyridinium-N-phenol betaine.

7. The vapor-grown-carbon-fiber-containing dispersion as recited in anyof 1 through 6 above, wherein the organic solvent has an ET value of 45or less and has a structure which is partially cyclic, where the ETvalue is a solvent parameter calculated from the absorption spectrum ofpyridinium-N-phenol betaine.

8. The vapor-grown-carbon-fiber-containing dispersion as recited in anyof 1 through 7 above, wherein the organic solvent is any oftetrahydrofuran (THF), N-methylpyrrolidone, benzene, toluene,cyclohexane, γ-butyrolactone, butyl cellosolve, or a mixture thereof.

9. The vapor-grown-carbon-fiber-containing dispersion as recited in 1above, wherein the ratio (by mass) of vapor grown carbon fiber to resinsoluble in organic solvent is “carbon fiber”: “resin soluble in organicsolvent”=0.1 to 80:20 to 99.9, and the resin content in the dispersionis 0.1 to 60 mass %.

10. A method for preparing a dispersion containing vapor grown carbonfiber, comprising a step of dissolving a resin in an organic solvent,adding thereto vapor grown carbon fiber having a fiber diameter of 0.001to 5 μm and an aspect ratio of 5 to 15,000, and subjecting the resultantmixture to stirring and/or ultrasonication.

11. A method for preparing a dispersion containing vapor grown carbonfiber, comprising a step of mixing a resin soluble in an organic solventand vapor grown fine carbon fiber having a fiber diameter of 0.001 to 5μm and an aspect ratio of 5 to 15,000, and adding the resultant mixtureto an organic solvent.

12. A method for producing a resin composite material containing vaporgrown carbon fiber, characterized by applying a vapor grown carbon fiberdispersion as described in any of 1 through 9 above to a substratematerial, followed by removal of the solvent.

13. A resin composite material containing vapor grown carbon fiber,produced by the method as recited in 12 above.

14. An electroconductive material including a resin composite materialobtained by the method as recited in 12 above.

15. A thermal conductive material including a resin composite materialobtained by the method as recited in 12 above.

The carbon fiber which may be used in the present invention is vaporgrown carbon fiber having a fiber diameter of 0.001 μm to 5 μm and anaspect ratio of 5 to 15,000. Preferred examples of such a carbon fiberinclude carbon fiber grown from the vapor phase, which fiber may beproduced by blowing, in a high temperature atmosphere, a gaseous organiccompound together with iron or a similar element serving as a catalyst(see Japanese Patent No. 2778434).

The carbon fiber grown from the vapor phase (the vapor grown carbonfiber) may be, for example, “as-produced” carbon fiber; carbon fiberobtained through thermal treatment of “as-produced” carbon fiber at 800to 1,500° C.; or carbon fiber obtained through graphitization of“as-produced” carbon fiber at 2,000 to 3,000° C. Preferably, the vaporgrown carbon fiber is thermally treated at around 1500° C. orgraphitized at 2,000 to 3,000° C. before use.

During the graphitization process, an element such as B, Al, Be or Si,preferably B, promoting the crystallization of carbon may be added tothe vapor grown carbon fiber, to thereby produce vapor grown carbonfiber, wherein the carbon crystals of the fiber contain a small amount(0.001 to 5 mass %, preferably 0.01 to 2 mass %) of a crystallizationpromoting element (WO00/585326).

The resin to be used for forming a dispersion of the present inventionmay be a thermoplastic resin, a thermosetting resin or any other type ofresin, so long as it is soluble in an organic solvent. The resin solublein an organic solvent may be a resin including a polymer having astructural repeating unit which at least partially contains a cyclicstructure. The cyclic structure may contain, in addition to carbonatoms, oxygen, nitrogen or sulfur atoms.

Examples of the resin include polystyrene, polycarbonate (PC),polyarylate (PAR), polysulfone, polyether-imide, polyethylene sulfide,polyphenylene sulfide (PPS), polyethylene terephthalate (PET),polybutylene terephthalate (PBT), polyimide, polyamidoimide,polyether-ether-ketone, modified polyphenylene oxide and polyamic acid.Preferred examples of the resin include polystyrene, polycarbonate,polyarylate, polysulfone, polyether-imide, polyethylene sulfide,polyphenylene sulfide, polybutylene terephthalate, polyimide,polyamidoimide, polyether-ether-ketone, polyamic acid and mixturesthereof.

The ratio (by mass) of vapor grown carbon fiber to resin soluble inorganic solvent varies depending on the intended use of the resincomposite material. Generally, the ratio; i.e., carbon fiber: resinsoluble in organic solvent, fall within the range of 0.1:99.9 to 80:20,and the resin content of the dispersion is 0.1 to 60 mass %. When theamount of vapor grown carbon fiber is less than 0.1 mass %, satisfactoryelectroconductivity or thermal conductivity of the composition cannot beobtained after removal of solvent, whereas when the amount of fiber isin excess of 80 mass %, the resin coating composition obtained from theresin dispersion is apt to be brittle.

The organic solvent employed as the dispersion medium in the presentinvention preferably has an ET value of 45 or less, where the ET valueis a solvent parameter calculated from the absorption spectrum ofpyridinium-N-phenol betaine (“Shin-jikken Kagaku Koza” (“NewExperimental Chemistry”) 14 (V), 2594 (1978)); Ann., 661, 1 (1963)).Preferred examples of the solvent include dichloromethane, chloroform,dimethoxyethane, ethyl acetate, bromobenzene, chlorobenzene,tetrahydrofuran (THF), anisole, dioxane, diethyl ether, benzene, carbontetrachloride, toluene, cyclohexane, hexane and isooctane. Morepreferred solvents have a cyclic structure and examples thereof includetetrahydrofuran (THF), N-methylpyrrolidone, benzene, toluene,cyclohexane and γ-butyrolactone.

No particular limitations are imposed on the proportions of vapor growncarbon fiber, resin (solute) and dispersion medium. Preferably, thesolute resin is incorporated in an amount of 60 mass % or less so as tofacilitate dispersion.

No particular limitations are imposed on the dispersion method. Forexample, by dissolving resin in an organic solvent, adding vapor growncarbon fiber thereto, and then subjecting the mixture to stirring orultrasonication, a stable dispersion can be produced.

The state of dispersion differs depending on the condition of vaporgrown carbon fiber. Generally, before being dispersed, individualfilaments of vapor grown carbon fiber are not separated from oneanother. Rather, they exist as an agglomerate having a diameter of about100 μm. When such vapor grown carbon fiber is dispersed by the presentmethod, individual filaments of the vapor grown carbon fiber areseparated from each other in the resultant dispersion. Or, the resultantdispersion may contain agglomerates each having a diameter of about 40μm or less and individual carbon fiber filaments in an intermingledstate.

Polycarbonate employed as resin, to which vapor grown carbon fiberhaving a fiber diameter of 0.15 μm and an aspect ratio of 70 and havingundergone a heat treatment at 2,800° C. had been added in an amount of 5mass %, was incorporated into benzene (BZ, ET value=34.5),tetrahydrofuran (THF, ET value=37.4) dichloromethane (DCM, ETvalue=41.1), dimethylformamide (DMF, ET value=43.8), or acetonitrile(ATN, ET value=46.0) to thereby prepare 10 mass % dispersions of theresin, followed by stirring for 30 minutes with a stirrer. In the casewhere the organic solvent is any of benzene, tetrahydrofuran,dichloromethane and dimethylformamide, the resultantvapor-grown-carbon-fiber-containing dispersion does not causeprecipitation of vapor grown carbon fiber even after being left to standfor one week. In contrast, in the case where the organic solvent isacetonitrile, the resultant dispersion starts to precipitate on thesecond day, producing a clear supernatant.

Applying the dispersion of the present invention to a substrate (such asa circuit board) by the coat drying method (in which after coating, thesolvent contained therein is evaporated by drying) enables to obtain aresin composite material in which vapor grown carbon fiber is uniformlydispersed. Thus-obtained materials are endowed with excellentelectroconductivity and thermal conductivity. For applying thedispersion of the present invention to a substrate, conventional methodsfor coating a paste or dispersion may be employed; for example, coatingmay be formed through use of a doctor blade, screen printing or spincoating. For drying the solvent of the coating, conventional methodscustomarily employed for evaporating solvents, such as heat drying andvacuum drying, can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A) and 1(B) are optical micrograph images respectively of aPC/THF-based dispersion of VGCF and a PS/THF-based dispersion of VGCF.

FIGS. 2(A) and 2(B) are optical micrograph images respectively of thinfilms formed through spin coating of a PC/THF-based dispersion of VGCFand formed through spin coating of a PS/THF-based dispersion of VGCF.

FIGS. 3(A) and 3(B) are optical micrograph images respectively of aPS/BZ-based dispersion of VGCF and a PS/DMF-based dispersion of VGCF.

FIGS. 4(A) and 4(B) are optical micrograph images respectively of thinfilms formed through spin coating of a PS/BZ-based dispersion of VGCFand formed through spin coating of a PS/DMF-based dispersion of VGCF.

FIG. 5 is an optical micrograph image of a dispersion of VGCF in a mixedsolution of polyamic acid/N-methyl-2-pyrrolidone, γ-butyrolactone andbutyl cellosolve.

FIGS. 6(A) and 6(B) are optical micrograph images respectively ofdispersions of VGCF in THF (A) and in DCM (B).

FIGS. 7(A) and 7(B) are optical micrograph images respectively ofdispersions of VGCF in BZ (A) and in DMF (B).

FIG. 8 is an optical micrograph image of a PS/ATN-based dispersion ofVGCF.

FIG. 9 is an optical micrograph image of a PMMA/THF-based dispersion ofVGCF.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will next be described by way of examples andcomparative examples, which should not be construed as limiting theinvention thereto.

EXAMPLE 1

A 10 mass % solution of polycarbonate (PC; product of Teijin ChemicalsLtd., AD5503; number average molecular weight=20,000, mass averagemolecular weight=32,000) in tetrahydrofuran (THF) was prepared. To thesolution, vapor grown carbon fiber (VGCF, registered trademark, productof Showa Denko K. K.) having a fiber diameter of 0.15 μm and an aspectratio of 70 and having undergone heat treatment at 2,800° C. was addedin an amount of 0.2 mass %, followed by mixing with a mechanical stirrerat 600 rpm for 30 minutes. A dispersion in which the vapor grown carbonfiber was uniformly dispersed was obtained. After the dispersion wasleft to stand for seven days at room temperature, precipitation of vaporgrown carbon fiber was not observed. Observation under an opticalmicroscope confirmed that individual filaments of VGCF (registeredtrademark) were quite excellently dispersed. Spin coating was performedby applying several droplets of the dispersion onto a cover glass androtating the cover glass at 100 rpm for 5 seconds, 1,000 rpm for 10seconds, and 100 rpm for 5 seconds, whereby thin film of compositematerial was produced. The resultant thin film was found to contain VGCF(registered trademark) in an excellently dispersed manner.

Similarly, thin film was produced by use of a dispersion and the spincoating method, except that the above-employed polycarbonate (PC) wasreplaced by polystyrene (PS; product of Asahi Kasei, PS666, numberaverage molecular weight=420,000, mass average molecularweight=1,000,000). FIGS. 1 and 2 show optical micrograph images of thedispersions and thin films obtained.

EXAMPLE 2

The combination of polystyrene (PS) and THF employed in Example 1 wasmodified to use benzene (BZ) or dimethylformamide (DMF) instead of THF,to thereby produce a dispersion and form a thin film through spincoating.

FIGS. 3 and 4 show optical micrograph images of the dispersions and thinfilms obtained.

EXAMPLE 3

A solution was prepared by dissolving 5 mass % polyamic acid (which is aprecursor of polyimide) in a solvent prepared by mixingN-methyl-2-pyrrolidone, γ-butyrolactone, and butyl cellosolve atproportions of 30:30:35 by mass % and adding thereto. VGCF (registeredtrademark) was added to the solution in an amount of 2 mass % or 5 mass% on the basis of polymer, followed by stirring at 200 rpm for 20minutes with a magnetic stirrer. The mixture was left to stand at roomtemperature for 7 days. Both of the dispersion containing 2 mass % VGCF(registered trademark) and the dispersion of 5 mass % VGCF (registeredtrademark) were found to be free from precipitation of vapor growncarbon fiber. Observation under an optical microscope confirmed thatindividual filaments of VGCF (registered trademark) were quiteexcellently dispersed. The optical micrograph is shown in FIG. 5. A thinfilm of a composite was formed through spin coating by applying severaldroplets of the dispersion onto a cover glass and rotating the coverglass at 100 rpm for 5 seconds, 1,000 rpm for 10 seconds and 100 rpm for5 seconds. The resultant thin film was found to contain VGCF (registeredtrademark) in an excellently dispersed manner.

EXAMPLE 4

The vapor-grown-carbon-fiber-containing dispersion prepared in Example 1was applied onto a substrate of circuit board through screen printing,then dried with air, to thereby produce a coating film of avapor-grown-carbon-fiber-containing composite. Electroconductivity ofthe coating film was evaluated (Evaluation Sample No. 1). Separately,coating films were formed by varying the amounts of polycarbonate andvapor grown carbon fiber as shown in Table 1 (Evaluation Sample Nos. 2to 4). Furthermore, another coating film was formed through use ofpolystyrene (PS; product of Asahi Kasei, PS666, number average molecularweight=420,000, mass average molecular weight=1,000,000) instead ofpolycarbonate, and electroconductivity of the resultant sample(Evaluation Sample No. 5) was evaluated. The results are shown in Table1.

COMPARATIVE EXAMPLE 1

VGCF was added in each solvent of tetrahydrofuran (THF), dichloromethane(DCM), benzene (BZ) and dimethylformamide (DMF), so as to attain a VGCF(registered trademark) concentration of 0.2 mass %. Each mixture wasstirred with a mechanical stirrer at 600 rpm for 30 minutes, to therebyyield a dispersion. The dispersion was sandwiched between a slide glassand a cover glass, and placed under an optical microscope forobservation of the dispersion state of VGCF (registered trademark) at amagnification of ×400. Initially present lumps of VGCF (registeredtrademark) were still observed. After the dispersion was left to standat room temperature, precipitation of vapor grown carbon fiber wasobserved on the second day. FIGS. 6 and 7 show optical micrograph imagesof the dispersions.

COMPARATIVE EXAMPLE 2

The solvent THF employed in Example 2 was replaced by acetonitrile(ATN), to thereby produce a dispersion. FIG. 8 shows an opticalmicrograph image of the dispersion.

COMPARATIVE EXAMPLE 3

The resin PC employed in Example 1 was replaced bypolymethylmethacrylate (PMMA; product of Asahi Kasei, 60N, numberaverage molecular weight=76,000, mass average molecular weight=150,000),to thereby produce a dispersion. FIG. 9 shows an optical micrographimage of the dispersion. TABLE 1 Concentration in dispersionThermoplastic Vapor grown Volume resin/concentration carbon fiberresistivity No. (mass %) (mass %) (Ωcm) 1 polycarbonate/10 0.2  10¹⁰ 2polycarbonate/40 10 10¹ 3 polycarbonate/30 20 10⁰ 4 polycarbonate/20 3010⁰ 5 polystyrene/40 10 10¹

INDUSTRIAL APPLICABILITY

The present invention enables to produce a resin solution in which vaporgrown carbon fiber is uniformly dispersed, through use of vapor growncarbon fiber having a fiber diameter of 0.001 to 5 μm and an aspectratio of 5 to 15,000, a resin which is soluble to an organic solvent,and a nonpolar solvent having an ET value of 45 or less as an organicsolvent, where the ET value is a solvent parameter calculated from theabsorption spectrum of pyridinium-N-phenol betaine. Electroconductivematerials and thermal conductive materials can be readily obtained fromthe dispersion by, for example, coating.

1. A vapor-grown-carbon-fiber-containing dispersion containing vaporgrown carbon fiber having a fiber diameter of 0.001 to 5 μm and anaspect ratio of 5 to 15,000, a resin soluble in an organic solvent andan organic solvent, wherein lumps of the carbon fiber are partiallydisintegrated to thereby allow separated individual filaments of thecarbon fiber to be present as dispersed.
 2. Avapor-grown-carbon-fiber-containing dispersion containing vapor growncarbon fiber having a fiber diameter of 0.001 to 5 μm and an aspectratio of 5 to 15,000, a resin soluble in an organic solvent and anorganic solvent, wherein the carbon fiber is present such that carbonfiber lumps having a diameter of 40 μm or less and separated individualcarbon fiber filaments are intermingled.
 3. Thevapor-grown-carbon-fiber-containing dispersion as claimed in claim 1 or2, wherein the vapor grown carbon fiber contains 0.001 to 5 mass % ofboron.
 4. The vapor-grown-carbon-fiber-containing dispersion as claimedin claim 1 or 2, wherein the resin soluble in an organic solvent is aresin comprising a polymer having a structural repeating unit which atleast partially contains a cyclic structure.
 5. Thevapor-grown-carbon-fiber-containing dispersion as claimed in claim 1 or2, wherein the resin soluble in an organic solvent is any ofpolystyrene, polycarbonate, polyarylate, polysulfone, polyether-imide,polyethylene terephthalate, polyphenylene oxide, polyphenylene sulfide,polybutylene terephthalate, polyimide, polyamidoimide,polyether-ether-ketone, or polyamic acid, or a mixture thereof.
 6. Thevapor-grown-carbon-fiber-containing dispersion as claimed in claim 1 or2, wherein the organic solvent has an ET value of 45 or less, where theET value is a solvent parameter calculated from the absorption spectrumof pyridinium-N-phenol betaine.
 7. Thevapor-grown-carbon-fiber-containing dispersion as claimed in claim 1 or2, wherein the organic solvent has an ET value of 45 or less and has astructure which is partially cyclic, where the ET value is a solventparameter calculated from the absorption spectrum of pyridinium-N-phenolbetaine.
 8. The vapor-grown-carbon-fiber-containing dispersion asclaimed in claim 6, wherein the organic solvent is any oftetrahydrofuran (THF), N-methylpyrrolidone, benzene, toluene,cyclohexane, γ-butyrolactone, butyl cellosolve, or a mixture thereof. 9.The vapor-grown-carbon-fiber-containing dispersion as claimed in claim1, wherein the ratio (by mass) of vapor grown carbon fiber to resinsoluble in organic solvent is “carbon fiber”: “resin soluble in organicsolvent”=0.1 to 80:20 to 99.9, and the resin content in the dispersionis 0.1 to 60 mass %.
 10. A method for preparing a dispersion containingvapor grown carbon fiber, comprising a step of dissolving a resin in anorganic solvent, adding thereto vapor grown carbon fiber having a fiberdiameter of 0.001 to 5 μm and an aspect ratio of 5 to 15,000, andsubjecting the resultant mixture to stirring and/or ultrasonication. 11.A method for preparing a dispersion containing vapor grown carbon fiber,comprising a step of mixing a resin soluble in an organic solvent andvapor grown fine carbon fiber having a fiber diameter of 0.001 to 5 μmand an aspect ratio of 5 to 15,000, and adding the resultant mixture toan organic solvent.
 12. A method for producing a resin compositematerial containing vapor grown carbon fiber, characterized by applyinga vapor grown carbon fiber dispersion as claimed in claim 1 to asubstrate material, followed by removal of the solvent.
 13. A resincomposite material containing vapor grown carbon fiber, produced by themethod as claimed in claim
 12. 14. An electroconductive materialincluding a resin composite material obtained by the method as claimedin claim
 12. 15. A thermal conductive material including a resincomposite material obtained by the method as claimed in claim 12.